Molding process and product thereof



Dec. 11., 1945. c. w. EGAN MOLDING PROCESS AND PRODUCT THEREOF Filed July 13, 1944 MlXING 5TEP- EXTRUDlNC-l STEP SHREDDING 5TEP w W W 3 p E T 5 a m o L o M a P E T s a m K A a a CHARLIE. 5W E. BAN,

Patented Dec. 11, 1945 MOLDING PROCESS AND PRODUCT THEREOF Charles W. Egan, Troy, N. Y. Application July 13, 1944, Serial No. 544,741

3 Claims. (Cl. 18-475) (Granted under the act of March 3, 1883, as amended April 30, 1928; 370 0. G. 757) The invention described herein may be manufactured and used by or for the Government for governmental purposes, without the payment to me of any royalty thereon.

This invention relates to improvements in molding processes and is directed more particularly to a process for molding a so-called gascheck or obturator pad.

In some weapons or guns, particularly of the heavy type using separate-loading ammunition, it is usual to provide some device to prevent the powder gases from passing to the rear and into the breech mechanism thereof, principally in order to avoid erosion of the threads and other parts. To this end, a so-called gas-check, or obturator pad is invariably provided for location in the breech block in a manner which forms no part of this invention.

It is common practice to form such pads from a pressed mixture of asbestos, tallow, paraffin, and some solvent so as to provide a plastic pad that melts only at a high temperature. The arrangement of the pad and obturator parts is such that the elastic pad is compressed during operation of the weapon in such a way as to effectually prevent the passage of gas to the rear.

It will be obvious that such a pad must not only be sufiiciently flexible to perform its desired function but it must not tend to be fluid or otherwise deteriorate. I have found that the common practice of including a solvent in the pad-forming composition creates this objectionable tendency to fluidity and deterioration, as well as having other disadvantages.

It is accordingly a principal object of this invention to provide a gas-check or obturator pad for use in firearms which has the capacity to withstand high pressures and temperatures for a greater length of time than such pads as have hitherto been known. As will appear, this is accomplished by means of a novel process which not only obviates the use of the usual solvent but it has a special advantage in that it does not require in its construction materials which are extremely critical in times of war, yet at the same time a durable, sufliciently flexible pad is produced.

As stated, it has long been common to employ a mechanical mixture of asbestos fibre, tung oil, tallow, Vaseline, and other ingredients, to press the mixture into the shape of a core and provide the core with some form of a wrapping. Such pads hitherto manufactured, it will be seen, not only require the use of critical materials but they have failed in service for various reasons, particularly in that under varying rapid rates of fire they soften and become more or less fluid so as to present a surface with relatively no wear resistance. The result is that they aiford relatively less resistance to the gas passage.

It is, then, one of the objects of this invention to provide a process whereby the product resulting therefrom does not tend to soften as rapidly as prior-art pads but at the same time it is much more resilient and dimensionally stable under wide variations of humidity and pressures than pads made in the ordinary way.

Accordingly, too, it is a special advantage of the process of this invention that the basic mix from which the pads are made does not require the use of a solvent. That is to say, the novel process is such that the desired homogeneous mass is brought about without the introduction of the critical and deterioration-causing or fluidifying solvents which have heretofore always been employed.

The specific nature of this invention as well as other objects and advantages thereof will clearly appear from a description of a preferred embodiment as shown in the accompa ying drawing in which:

Fig. 1 is a elevational view, partly in section, of an obturator pad constructed in accordance with this invention.

Fig. 2 is a sectional view of the pad shown in Fig. 1 taken along the plane 2-2 thereof.

Fig. 3 is a schematic view illustrating the various steps of a process in accordance with this invention by which the improved obturator pad may be produced.

The actual physical construction of the pads of this invention does not vary appreciably from prior practices and therefore does not form a part of this invention. However, for purposes of a more complete understanding of this invention, it will be said that essentially a core is eventually formed, and then pressed into a. screenwire form. It is also usual to paint the resulting article with shellac and then bake it.

According to this invention, and referring to Figs. 1 and 2, a pressed core I is formed of asbestos and a heat-polymerized oil and the same is provided with a covering of wire cloth 2 and then baked. It is generally desirable to coat the pad prior to baking with a varnish or shellac indicated at 3. The oil used is preferably a linseed oil and the preferred proportions of oil and fibre are approximately from 23 to 26 percent. of the oil and from 74 to 77 percent of the fibre.

The oil used in this invention, which, as stated,

is preferably a linseed "'oil, is extremely sticky and thick, having a Saybolt viscosity of say 37 minutes. The mixture of this oil and the asbestos, which is preferably a medium-light, commercial fibre, :becomes a lumpy mass and it will be noted no solvent is employed.

According to this process, the mixture of oil and asbestos 5 is eflected in a container 4. The lumps are forced continuously through some such means as a screw-feeder 6 and then extruded against a shredding means. This may take the form of a plurality of coarse wire brushes 1 operating at a great speed, against the faces of which the lumps are so urged that the oil-fibre mix is thoroughly shredded. The shredded mass is then molded into form and enveloped in the wire mesh 2 as indicated by the molding step 8 and the resulting form is then baked as indicated by the baking step 9.

This process results in the production of a mass of shredded material which is capable of being molded into an even more homogeneous mass than if a solvent had been employed. Further more, the baking of the core so molded can be done more rapidly than otherwise because there is no entrapped volatile matter to cause pressed material to swell, blister or otherwise go out of shape, as there is when the mixture contains a solvent or when it is merely pressed into the form of a core without the previous shredding step.

The coating applied to the form prior to baking should preferably constitute a varnish which is relatively flexible and capable of excluding air. Also the coating will preferably be alkali and acid resistant.

It has been found desirable to bake the pads at temperatures varying between 250 and 350 F. As contrasted with prior art practice, the baking according to this process only requires about two hours which is a relatively short time.

I claim:

1. As a new article of manufacture, a gas-check pad of the class described arranged to be disposed within the breech-block of a heavy-type weapon comprising, a core member consisting of a compressed baked shredded mass of asbestos fibers and a substantially nonvolatile, heat-polymerized oil, said mass being, substantially free from volatile solvents, and an enveloping member of substantially flexible material around said core member.

2. As a new article of manufacture, a gas-check pad of the class described arranged to be disposed within the breech-block of a heavy-type weapon comprising, a molded body member consisting of a shredded and baked mass of asbestos fibers and a substantially non-volatile, heat-polymerized 1inseed oil, and an enveloping member around said body member, said pad being substantially free of any entrapped volatile solvents.

3. The continuous process of making an obturator pad which is substantially free of entrapped volatile solvents and arranged to be disposed within the breech-block of a heavy-type weapon cvonsisting of, forming a mixture of asbestos fibers and a heat-polymerized oil without utilizing a solvent, shredding such mixture into small particles to achieve an intimate mixture of the oil and fibers and then compressing the shredded mass into the form of a core, and finally coating the core with a resinous and insulating substance and baking the coated core.

CHARLES W. EGAN. 

